Theater (cinema) movies are projected in various aspect ratios, where the aspect ratio is defined as the ratio of the width to the height of the projected image as seen on the screen. The most common aspect ratios are the conventional 1.85:1 “flat” image and the 2.35:1 “scope” image. Historically, most televisions and computer displays have a 1.33:1 aspect ratio. High-definition television typically has a 1.78:1 aspect ratio, and many modern televisions are produced with this screen aspect ratio.
Even though there are many aspect ratios in common use, and others may be introduced in the future, the images are typically recorded (i.e., stored) in a “native” format dictated by the physical dimensions of a film (if analog recording for analog playback) or a spatial light modulator (if digital recording for digital playback). The stored native format may have an aspect ratio different from that of the on-screen projected image. To accomplish the conversion between the aspect ratio of the stored native format and the aspect ratio of the on-screen projected format, the image may be projected through an anamorphic lens, in which the image is enlarged along a first transverse axis to a different extent than along a second, perpendicular transverse axis. That is, the recorded image may be asymmetrically stretched. Thus, for example, a 1.33:1 native format may be projected in a 1.85:1 on-screen format.
Available anamorphic lens structures used in cinema projectors are affixed to the existing lens structure of the projector forward of the objective lenses of the projector. Accordingly, the anamorphic lens structures must be large in diameter, and are consequently heavy and cumbersome. They change the balance and structural requirements of the projector when affixed to the projector.
The cinema normally must be equipped to project at least flat and scope movies. The projector lens structure must be changeable between these two formats. Additionally, some cinemas now are made available for business presentations or other uses requiring the projection of images, so that the projector must be capable of supporting 1.33:1 images or other formats. Existing projectors are difficult to convert between these various formats, at least partially because of the anamorphic lens structure.
These same problems may arise for recording devices, particularly digital recording cameras, that receive and record an image.
There is a therefore a need for improved optical systems for recording and projecting images, to permit conversion between different aspect ratios for the recording and projecting. The present invention fulfills this need, and further provides related advantages.